What is PAL (Phase Alternating Line)?

PAL (Phase Alternating Line) is the name used to indicate the encoding system used to transmit analog color television signals.

What is PAL (Phase Alternating Line)?

What is the PAL Video Format?

PAL system is used in most African, Asian, and European countries, as well as in Australia and some American countries.

This system was developed by Dr. Walter Bruch in Telefunken laboratories in 1963 to improve the quality and reduce imperfections in the color tones offered by the NTSC system.

However, the basic concepts of signal transmission are based on the NTSC system.

Features

The phase alternating line allows the transmission of chrominance information of a video signal, inverting in each line and phase, canceling each other, allowing possible errors in one phase to be automatically corrected.

In radiofrequency data transmission, phase errors are common and therefore caused by signal delays in arrival or processing. Phase errors in the analog video cause an error in color tone, adversely affecting image quality.

Taking advantage of the similarity of the color content of one line and the other, the receiver automatically compensates for color tone errors by taking the average value of one line and the other, given the possible phase error between the two.

This error is seen as a slight defect in color saturation that is much less detectable by the human eye, rather than a change in hue as in NTSC. This is the biggest advantage of the PAL system over the NTSC system.

The lines in which the phase is reversed from how it will be transmitted in NTSC are usually called PAL lines, and the ones to match are called NTSC lines. PAL’s operating system means it is a more complex application than the NTSC system.

This is because although the first receivers took advantage of human eye defects to cancel out phase errors, without the electronic correction described above, this resulted in a highly visible effect when the error exceeded 5º.

The luminance signal of about 64 µs, which serves to store the chrominance information of each received line, was solved with a delay in processing. The color average of one line and the next can be viewed on the screen.

Devices that could generate this latency were relatively expensive when PAL was introduced, but were later produced at low cost.

This solution reduced vertical color resolution compared to NTSC, but this effect was not very beneficial as the human retina is much less sensitive to color information.

NTSC televisions include a color tone corrector feature to manually perform this correction.

The PAL system is more consistent than the NTSC format, but NTSC is technically superior where the signal is transmitted without phase changes.

However, for this, there must be ideal transmission conditions between transmitter and receiver. PAL is clearly superior to NTSC whenever there are signal jumps.

It was one of the reasons most European countries chose this system because the European orography is much more complex than North America.

One of the other reasons is that local broadcasts are widespread in the USA and in Europe, where national stations tend to have wider coverage.

The only way NTSC is superior to PAL is because of its higher refresh rate, there is no flickering sensation that can be seen in the peripheral field of view when watching TV on a large screen.

NTSC and PAL

PAL-DVD (720×576) video has a higher resolution than NTSC-DVD (720×480). However, since the image of this format has more pixels, a higher compression factor is used when compressing to MPEG2, resulting in greater loss of quality.

On the other hand, since the compression factor is lower in NTSC, less quality loss is experienced compared to PAL.

Because NTSC has more than 5 frames per second, it performs better in scenes with a lot of movement on the screen or very fast movements on part of the screen.

MPEG2 compression has more frames, resulting in better results in these types. This format can be considered smoother since there is no duplicate space download.

Film cameras are 4% faster than PAL format as they run at 24 full frames, so there is a mismatch between image and sound but this is difficult to spot.

PAL causes more eye strain as it has more image flickering than NTSC. NTSC systems are less eye-tiring as they do not have the classic vibration operating at 50Hz/25 FPS.

Formats

The color system is commonly used in a video format of 625 lines per frame and a screen refresh rate of 25 frames per second.

Some Eastern European countries that stopped using the SECAM system used adaptations PAL-D or K to keep some of the technical aspects of SECAM in PAL.

In Brazil, the version PAL-M is used, with 525 lines and 29.97 frames per second, which is very close to NTSC in the color subcarrier frequency.

Brazil’s telecommunications regulator, Anatel, began using its own standard in the early 1970s to prevent the import of color receivers and ensure compatibility with monochrome receivers. NTSC tests conducted in the country in the ’60s showed that the color quality was lost when the signal was distributed over long distances.

All other countries that use the M standard for black and white use NTSC as their color system.

This is used in Argentina, Paraguay, and Uruguay with the 625-line standard system, but the color subcarrier frequency is very close to that of NTSC and these types are PAL-N and PAL-CN.

Video equipment manufacturers in some Latin American countries offer three standard receivers, NTSC-M, PAL-M, and PAL-N.

In Europe, new television receivers can display signals from all these systems.

Most of them can receive SECAM signals from Eastern Europe and the Middle East, usually outside France, with the exception of French manufacturers’ equipment.

Many are even able to display baseband NTSC-M standard signals via video inputs only for signals from a video player or game console.

Digital System

This system is analog, and in the 1980s there was an attempt to make equipment that digitizes the signal, but it did not succeed commercially.

Digital television uses color components in digital devices such as modern game consoles, computers, where R, G, and B or Y, RY and BY signals are transmitted by three different cables.

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